Preparation of motor gasoline from carbonaceous feed material



Jan. 4, 1955 Q A COGHLAN 2,698,782

PREPARATION OF MOTOR GASOLINE FROM CARBONACEOUS FEED MATERIAL Filed0G12. 6, 1950 '/-WAcT/a/VA raz g RRS.

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United States Patent O PREPARATION OF MOTOR GASOLINE FROM CARBONACEOUSFEED MATERIAL Charles A. Coghlan, Port Arthur, Tex., assignor to TheTexas Company, New York, N. Y., a corporation of Delaware ApplicationOctober 6, 1950, Serial No. 188,749

Claims. (Cl. 44-80) The present invention relates to the preparation ofhigh quality motor gasoline from carbonaceous feed materials,particularly undesired hydrocarbon stocks, and more specifically, isconcerned with effecting the essentially complete conversion of theentire carbonaceous feed into desired proportions of olenic and aromaticmotor gasoline fractions.

In accordance with the copending application, United States Serial No.188,693, filed October 6, 1950 (No. 32,863) in the naine of Frank J.Jenny, undesired liquid hydrocarbons, particularly heavy residual stocksof rela tively high carbon residue, which cannot be economicallyconverted by conventional thermal or catalytic methods, are subjected tothermal cracking in a flowing stream of partial combustion products,composed of a mixture of hydrogen and carbon monoxide, issuing from asynthesis gas generator substantially at combustion temperatures atleast about 2000 F. and up to 3000 F. and above, or higher. Pyrolyticdecomposition of the injected liquid hydrocarbon takes place at acracking temperature controlled by the relative rate of hydrocarbon feedinjection, or otherwise, to yield a preferably highly aromatic crackedgasoline fraction.

In the flowing stream of partial combustion gas, the solid carbonaceousresidues of cracking are liberated in the form of particles of dry andfluffy appearance which remain entrained in the gas stream and arecarried out of the reaction zone with the gasiform product effluent. Inthis way, coke or carbon deposition in the reactor is avoided.

The effluent products of reaction pass into a fractionation tower, wherethe desired fractions are separated,

while the upowing gases are continuously scrubbed by the downflow oilreflux, which continuously delivers the carbon particles to the bottomof the tower as a slurry in the heavy hydrocarbon residuum. This slurryof fine particle coke in the heavy bottom fraction is continuouslywithdrawn and subjected to partial combustion with regulated quantitiesof essentially pure oxygen to continuously supply the aforementionedstream of partial combustion gas which feeds the cracking zone.

Thus, the fractionator residuum, with the coke particle residue of thethermal cracking slurried therein, is continuously consumed in thegeneration of the high temperature partial combustion gasawhich, inturn, supports continuous thermal conversion of the cracking fraction,so that the entire hydrocarbon feed is continuously consumed toVextinction in the formation of desired liquid and gaseous fractions.

In accordance with the present invention, the normally gaseous fractionof the product eluent from the cracking zone, and including the streamof hydrogen and carbon monoxide from the partial combustion step, iscontinuously recovered from the fractionator. The separated fraction,rich in hydrogen and carbon monoxide, after further treatment, ifdesired, to separate light gaseous hydrocarbons and the like, iscontinuously contacted with an iron hydrocarbon-synthesis catalyst toform liquid, predominantly olefinic hydrocarbons in the motor gasolineboiling range. The desired ole-finie gasoline fractions are separatedfrom this synthesis etiluent, residual hydrocarbons passingcontinuouslyV as the cracking stock to the aforementioned pyrolyticconversion or cracking step. Preferably, the cracking step is operatedas above Y to yield highly aromatic liquid fractions. Accordingly,

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the undesired residual fractions of the synthetic olefinic hydrocarbonsare continuously converted into valuable aromatic gasoline fractions,while the heavy residues of cracking, including the solid carbonaceousparticles formed therein, are continuously disposed of in forming asynthesis gas mixture of hydrogen and carbon monoxide, which iscontinuously converted in the catalytic synthesis step to form theoleinic motor gasoline fraction and the cracking stock.

Aside from the benefits of complete consumption of the feed materials inthe continuous formation of desired motor gasoline fractions withelimination of the objectionable coking problem, the present inventionhas numerous additional advantages. More specifically, the simultaneousproduction of synthetic oletinic fractions and thermally crackedaromatic fractions in the motor gasoline boiling range enablescontinuous production of a blend which is ideal from the standpoint ofmotor fuel requirements.

Unfortunately, the motor gasoline boiling fractions formed by catalyticsynthesis from hydrogen and carbon monoxide alone, fail to meet theserequirements. With synthesis catalysts such as cobalt, the product isexclusively parafi'inic, whereas the synthesis product of an iron typecatalyst is predominantly oleiinic throughout its entire range.

Actually, a preferred motor gasoline is one that is predominantlyolefinic in the lower boiling portion of the range, as for example, upto about 220 F. and predominantly aromatic above. The present inventionmakes it possible to selectively realize this result by withdrawing asproduct the aromatic fractions boiling in the upper portion of the motorgasoline range and the olefinic products in the lower portion of thisrange, and continuously recycling remaining fractions to the crackingzone.

The conditions of thermal cracking conducive to maximum formation ofmotor gasoline boiling aromatics include relatively high temperatures of1100-1500" F. and a contact time of 1 to 10 seconds.

As above intimated, the carbonaceous feed to the partial combustion orsynthesis gas generation zone may include, in addition to the slurry ofsuspended cokirig particles in heavy liquid residuum, additionalhydrocarbons, such as all or any desired portion of the primary feedstream of carbonaceous material. While this primary feed may be anydesired liquid hydrocarbon fraction,'practical considerations dictateuse of some relatively low value fraction such as heavy residualfractions of relatively high carbon residue and low value forconventional cracking purposes. However, gaseous hydrocarbons may alsoconstitute the feed to the gas generation step, and therefore, theprimary feed to the process may comprise, or else consist exclusive ofhydrocarbon gases, such as methane, natural gas and waste refinerygases. So also, generation of the synthesis gas mixture of hydrogen andcarbon monoxide may be effected by the partial combustion of essentiallysolid carbonaceous materials containing hydrogen, as for example, coal,lignite, peat, etc. In general, feeds suitable for cracking go first tothe cracking step, the others passing directly to the partial combustionstep.

Referring now to the attached flow sheet, wherein one embodiment of thepresent invention is disclosed, a carbonaceous feed stock, such asnatural gas, enters from any suitable source not shown, through pipe 10leading into mixing burner 11. Pipe 10 also receives from branch pipe 15a heavy, high carbon residue slurry containing suspended solid residuesof coking, as will be hereinafter described in greater detail.

At the burner 11, the hydrocarbons meet a stream of substantially pureoxygen, of at least percent and preferably percent purity, or higher,which is introduced from a suitable source, not shown, through pipe 12.

As indicated, the burner discharges into a refractorylined combustionchamber 14 where the reactants undergo partial combustion to form aproduct gas composed essentially of hydrogen and carbon monoxide.

To effect this result, the feed streams to the burner are carefullyregulated to maintain the atomic O/C ratio of -the entering feedmaterials less than about 2:1, and preferably in the vicinity of about1:1 to about 15:1, since it is in this range that maximum yield of ahigh purity mixture of hydrogen and carbon monoxide results. Aspreviously stated, combustion is effected at a high temperature, as highas 3000 F. and above,'arid in any event, not substantially below about2000 F. When the hydrocarbon fed to burner 11 is natural gas, it isadvantageous to preheat the gas in order to maintain such temperatures.On the other hand, means are provided in the form of an inlet pipe 16for injecting into the mixing burner regulated quantities of steam tomoderate excessive combustion temperatures which would attack thechamber 14. Steam injection is particularly advantageous with a feedcomprising or composed of heavy residual stocks which burn with a highrate of heat release.

While the combustion Zone 14 is operable at atmospheric pressure, it isadvantageous in most cases to maintain therein substantiallysuperatmospheric pressures, as

for example, from 100 to 600 p. s. i. g. and preferably from 200 to 500p. s. i. g.

The substantial stream of synthesis gas from the combustion zone 14passes, without substantial cooling, through constriction 17 intocracking zone 18 at substantially the combustion temperature. Intocracking chamber 18, there is also injected, through pipe 19, theaforementioned heavier, synthetic hydrocarbon fractions, the grigi? ofwhich is to be hereinafter described in greater etai The rate of oilinjection through line 19 is such as to continuously maintain in thechamber a cracking temperature of, for example, 1100 to 1500 F. Crackingtakes place, therefore, in a substantial carrier stream of partialcombustion gases. Residence time in the cracking zone is from about 1 to10 seconds, preferably above about 2 seconds, such that predominantlyaromatic, pyrolytic conversion products in the gasoline boiling rangeare produced.

As indicated in the drawing, the cracking or pyrolytic conversionchamber 14 is preferably free, refractorywalled space, completely freefrom packing, partitions, checkerwork or any other internalobstructions.

As a result of this free and open internal space, the low area ofconfining wall surface, and the substantial flow rate of combustion gasthrough chamber 14, solid carbon or coke resulting from cracking occursin the form of ne dry, and somewhat fluffy appearing particles which,instead of being deposited within or upon the walls of chamber 18,remain entrained in the efuent gasiform stream of cracking products andcarrier gas.

The entire product effluent continuously passes through l transfer pipe20, through cooling exchanger 22 where its temperature range is reducedbelow about 650 F., and thereafter is injected into the lower portion ofthe fractionator 24.

The normally gaseous fractions of this effluent pass upt wardly throughfractionation column 24, countercurrent to the constant downow of oilreflux in the tower. Therefore, the gaseous stream is effectivelyscrubbed of the entrained solid particle carbonaceous materials, andissues overhead through pipe 25 free of solid particles.

As a further result of this scrubbing action, all the solid pyrolyticresidue ultimately descends to form a slurry with the tower bottoms.Accordingly, the tower bottoms, withdrawn through pipe 26, containsubstantially all the coking residue of solid carbon particles slurriedin the bottoms, tar and other heavy residuum. This passes, as indicated,into the aforementioned pine 15, which merges with the rst mentionedpipe 10, feeding the burner 11. Advantageously, therefore, the withdrawnbottoms fraction is restricted to high carbon residue fractions whichare particularly disadvantageous for thermal cracking, and, therefore,an indicated feed for partial combustion.

The desired, highly aromatic motor gasoline fraction is continuouslydrawn off as a side stream from tower Z4 through pipe 28 for blendinginto a nal product gasoline,

as' will hereinafter more fully appear. For example, the withdrawn sidestream may be approximately a 2204100o F. cut, of predominantly aromaticproduct.

A second side stream, preferably a 400-700 F. cut gas oil withdrawn fromtower 24 by pipe 30, passes into o To effect the foregoing results,reboiler 32 is advantageously provided in the bottom of the tower, andadditional refluxing is provided by withdrawing a side stream from thetower through line 33, pump 34 and cooling exchanger 35, and returningit at a higher point in the tower. Accordingly, therefore, thefractionator 24 continuously functions to deliver a desired productgasoline fraction, and to segregate the remainder into a normallygaseous overhead, relatively low carbon residue recycle fractions and anultimate bottoms slurry, containing substantially all the coking residueof thermal cracking.

rfhe overhead, normally gaseous fraction is withdrawn through pipe 25and preferably treated for removal of light gaseous hydrocarbons,methane, ethane, ethylene and the like, leaving a high grade, relativelypure stream of synthesis gas. Gas separation plant 36 is provided forthis purpose. Separation may be effected, for instance, by absorption oflight hydrocarbons in a suitable oil fraction, or even in an activated,absorbent material, the details of which, per se, form no part of thepresent invention. The separated hydrocarbon stream may passcontinuously through pipe 37 to supplement the hydrocarbon feed tomixing burner 11.

The resulting synthesis gas mixture of hydrogen and carbon monoxideflows through pipe 33 into reactor 39, where it passes in contact with ahydrocarbon synthesis catalyst. As indicated, the synthesis reactor 38comprises an upstanding chamber containing a preferably fluidized massof solid particle catalyst 40. A heat exchanger bundle 41, immersed inthe fluidized mass of catalyst, is internally supplied with coolant tocontrol reaction teinperature.

The catalyst 40, preferably comprises an iron type, hydrocarbonsynthesis catalyst which characteristically converts hydrogen and carbonmonoxide into desired, predominantly olefinic products. For thispurpose, the operating temperature is held in a critical, narrow rangewhich may vary with the specific catalyst employed, but which is usuallybetween 550 and 700 F., typically about 650 F. Operating pressures arein the range of about 150 to 600 p. s. i. g., usually 200 to 400 p. s.i. g. The eluent gasiforn. products of reaction disengage from the uppersurface of the catalyst and pass outwardly through transfer line 42, andcooling exchanger 43, into condenser 44, from which aqueous condensateis drained via line 45.

The resulting oil condensate, as well as the normally gaseous efuent,pass through pipe 47 into fractionator 43, operating to deliver throughpipe 50 a lower end motor gasoline cut, with an end point, for example,of about 220 F. This fraction blended, as indicated, with the aromatic,220-400" F. motor gasoline boiling cut in pipe 2S, yields valuable motorgasoline, predominantly aromatic in the higher boiling range andpredominantly oletinic in the lower boiling range.

Referring now to the other product fractions separated in column 48, anoverhead of light gaseous hydrocarbons, together with some byproductcarbon dioxide from the hydrocarbon synthesis step, passes through line51 into line 37, feeding the mixing burner 11 of the partial combustionchamber 14. The C3-C4 olefin fractions are withdrawn through pipe 53 topolymerization plant S4, yielding additional quantities of desirablepolymer gasoline fractions which flow into the product blend throughpipe 55. Undesired residues from the polymerization plant 54 passthrough line 56 into pipe S1.

rfhe residual fractions boiling above 220 F. accordingly comprise thetower bottoms withdrawn through line 57 and these, as indicated,continually cycle into pipe 19, as the previously mentioned feed to thecracking Zone 18.

Accordingly, the present process functions continuously to converthydrocarbon fractions, unsuitable for cracking by ordinary means, into apartial combustion gas which is, in turn, converted into a synthetic,olefinic motor gasoline and thermal cracking stock. The syntheticthermal cracking stock is continuously subjected to pyrolytic conversionto form valuable aromatic fractions by continuous injection into the hotstream of partial combustion gas. The solid residue of coking whichaccompanies the pyrolytic conversion, therefore, occurs in the form ofsolid particles which pass off with the cracking products and arerecovered as a slurry in the residual hydrocarbon fractions thereof.These high carbon residue materials, as well as otherwise waste gaseousproduct streams, are continuously consumed to extinction in theformation of the high ternperature partial combustion or synthesis gaswhile the relatively low carbon residue hydrocarbon liquids outside thedesired boiling range are continuously supplied as thermal crackingfeed.

It is apparent from the foregoing that the invention is not limited tothe recovery of the specific nal product fractions above mentioned forpurposes of illustration, since various other product requirements mayalso be met. For example, according to one aspect of the invention, itis contemplated recovering as final product the entire motor gasolineboiling fractions from both the cracking and the hydrocarbon synthesisefluents. In any event, however, the residual, relatively low carbonresidue liquids form the pyrolytic conversion feed, While theexcessively high carbon residue products are consumed to extinction inthe formation of high temperature synthesis gas cracking medium.

As above indicated, the fresh feed of natural gas mentioned in theillustrative embodiment may be substituted in part or in its entirety byany suitable liquid or even solid fraction, such as a residual fuel oilor the like. Advantageously, with a liquid hydrocarbon feed, a portion,at least, thereof, is diverted through branch pipe 58 into thefractionating tower 24 to provide additional reflux and increase thevolume of liquid bottoms sufficiently to maintain desirable fluidity ofthe slurry. This procedure is particularly advantageous where the feedintroduced through pipe contains appreciable low carbon residueconstituents recoverable through pipe 30 and/or 31 as a desirable feedto the cracking zone.

It is particularly desirable, in order to prevent carbon deposition inthe cracking chamber 18, that the linear velocity of the carrier gasflow be held at a substantial level, as for instance, 1/2 to 10 feet persecond, preferably l to 6 feet per second.

The term high carbon residue, as used herein, refers to stocks which arerelatively unsuitable for cracking and are therefore, moreadvantageously consumed in the gas generation zone. The low carbonresidue stocks referred to are those having a relatively lower carbonresidue value, which yield substantial proportions of cracked motorgasoline fractions by the pyrolytic steps disclosed herein. In general,streams with a Conradson number below about 5 fall within the lattercategory, while those with a Conradson number materially above 5 aregenerally considered to be high carbon residue materials.

Reference is made to the aforementioned application, Serial No. 188,693,as regards the specific conditions of partial combustion, thermalcracking and the recovery and disposition of the solid products ofcoking.

Obviously, many modifications and variations of the invention as aboveset forth may be made without departing from the spirit and scopethereof, and therefore, only such limitations should be imposed as areindicated in the appended claims.

I claim:

1. A process for the production of a motor gasoline which comprisessubjecting a hydrocarbon to reaction with oxygen at a temperature aboveabout 2,000" F. in a synthesis gas generation zone to produce a streamof synthesis gas consisting essentially of hydrogen and carbon monoxide,injecting a hydrocarbon liquid cracking stock into said stream ofsynthesis gas at substantially said reaction temperature in a crackingzone to form a resulting mixture having a temperature in the range offrom about 1,100 to about 1,500 F. eiecting substantial thermal crackingof said stock with the formation of a cracked product comprising anaromatic fraction boiling within the motor gasoline boiling range,separating said aromatic fraction from the resulting product of saidcracking, passing carbon monoxide and hydrogen from said cracking zoneto a hydrocarbon-synthesis reaction zone, converting said carbonmonoxide and hydrogen in the presence of an iron-type hydrocarbonsynthesis catalyst into synthetic hydrocarbons comprising an olenicfraction boiling Within the motor gasoline boiling range and a higherboiling fraction, separating said higher boiling fraction from theresulting products of said synthesis reaction, supplying said higherboiling fraction to said cracking zone as cracking stock, separatingsaid olefinic fraction from the products of said synthesis reaction,blending said oleiinic fraction with said aromatic fraction to produce amotor gasoline fraction.

2. A process as defined in claim l wherein a contact time Within therange of 1 to 10 seconds is maintained in said cracking zone.

3. A process as defined in claim 1 wherein said aromatic fraction has aboiling range of from about 220 to about 400 F. and said olenic fractionhas a boiling range below about 220 F.

4. A process as defined in claim 1 wherein said hydrocarbon-synthesis iselfected at a superatmospheric pressure and at a temperature in therange of 550 to 700 F.

5. A process as defined in claim 1 wherein liquid hydrocarbons from saidcracking zone boiling outside said gasoline boiling range fraction andbelow about 700 F. are supplied to said cracking zone as part of saidcracking feed, and residue from said cracking zone boiling above about700 F. is supplied to said synthesis gas generation zone to producecarbon monoxide and hydrogen.

References Cited in the file of this patent UNITED STATES PATENTS

1. A PROCESS FOR THE PRODUCTION OF A MOTOR GASOLINE WHICH COMPRISESSUBJECTING A HYDROCARBON TO REACTION WITH OXYGEN AT A TEMPERATURE ABOVEABOUT 2,000* F. IN A SYNTHESIS GAS GENERATION ZONE TO PRODUCE A STREAMOF SYNTHESIS GAS CONSISTING ESSENTIALLY OF HYDROGEN AND CARBON MONOXIDE,INJECTING A HYDROCARBON LIQUID CRACKING STOCK INTO SAID STREAM OFSYNTHESIS GAS AT SUBSTANTIALLY SAID REACTION TEMPERATURE IN A CRACKINGZONE TO FORM A RESULTING MIXTURE HAVING A TEMPERATURE IN THE RANGE OFFROM ABOUT 1,100 TO ABOUT 1,500* F. EFFECTING SUBSTANTIAL THERMALCRACKING OF SAID STOCK WITH THE FORMATION OF A CRACKED PRODUCTCOMPRISING AN AROMATIC FRACTION BOILING WITHIN THE MOTOR GASOLINEBOILING RANGE, SEPARATING SAID AROMATIC FRACTION FROM THE RESULTINGPRODUCT OF SAID CRACKING, PASSING CARBON MONOXIDE AND HYDROGEN FROM SAIDCRACKING ZONE TO A HYDROCARBON-SYNTHESIS REACTION ZONE, CONVERTING SAIDCARBON MONOXIDE AND HYDROGEN IN THE PRESENCE OF AN IRON-TYPE HYDROCARBONSYNTHESIS CATALYST INTO SYNTHETIC HYDROCARBONS COMPRISING AN OLEFINICFRACTION BOILING WITHIN THE MOTOR GASOLINE BOILING RANGE AND A HIGHERBOILING FRACTION, SEPARATING SAID HIGHER BOILING FRACTION FROM THERESULTING PRODUCTS OF SAID SYNTHESIS REACTION, SUPPLYING SAID HIGHERBOILING FRACTION TO SAID CRACKING ZONE AS CRACKING STOCK, SEPARATINGSAID OLEFINIC FRACTION FROM THE PRODUCTS OF SAID SYNTHESIS REACTION,BLENDING SAID OLEFINIC FRACTION WITH SAID AROMATIC FRACTION TO PRODUCE AMOTOR GASOLINE FRACTION.